1. Field of the Invention
The present invention relates to a disk drive for driving a disk-shaped recording medium, such as a floppy disk, and, more specifically, to a disk drive provided with a turntable capable of centering the central hub of a disk mounted thereon.
2. Description of the Related Art
A floppy disk has a flexible disk, i.e., a flexible magnetic recording medium, provided with a central metal hub. The metal hub is provided with a center hole and a drive hole. A disk drive for driving the disk for rotation is provided with a turntable provided with a magnet for attracting the metal hub of the disk, a center shaft projecting from the support surface of the turntable, and a drive pin supported on a plate spring or a swing arm so as to be able to project from the support surface of the turntable.
When a floppy disk is loaded into the disk drive, the center hole of the hub receives the center shaft of the disk drive, and the drive pin plunges into the drive hole immediately after the turntable has started rotation. Subsequently, a centering operation is executed to position the hub correctly on the turntable. During the centering operation, the center shaft comes into contact with the edge of the center hole from one direction and the drive pin comes into contact with the edge of the drive hole from the opposite direction as the turntable rotates, and the hub slides slightly on the support surface of the turntable.
In this centering operation, the hub comes into close contact with the support surface of the turntable upon the entrance of the drive pin into the drive hole of the hub, and is attracted by a large force by magnetic attraction. The hub must be caused to slide on the turntable against the magnetic attraction to bring the center shaft and the drive pin into contact with the edges of the center hole and the drive hole, respectively. This centering operation nips the flexible disk between magnetic heads to move the hub relative to the turntable.
If the magnetic heads are unable to exert sufficient pressure to the disk, the hub cannot be moved on the turntable and the centering operation cannot successfully be achieved. In a disk drive for driving the disk of a high-capacity floppy disk for rotation at several thousands revolutions per minutes, the moving speed of the magnetic heads relative to the disk is very high. Therefore, the magnetic heads cannot be pressed by a high pressure to the disk in view of suppressing the abrasion of the magnetic heads. In a disk drive which drives a disk for rotation at 2400 rpm, pressure exerted by the magnetic head on the disk is on the order of ten and some gram force or several gram force so that the magnetic heads will exert a very low resistance, i.e., torque, on the disk. Accordingly, this disk drive is unable to achieve a reliable centering operation for centering the hub on the turntable.